Leading critic of Rwandan President Paul Kagame faces accusations of forgery and tax evasion, police say.

Police in Rwanda have arrested Diane Shima Rwigara, a prominent government critic, charging her with forgery and tax evasion.

Her mother and sister were also held on Monday on the tax charges.

Earlier this year, electoral authorities barred Rwigara from standing in August's presidential vote, which President Paul Kagame won by a landslide, saying she had not submitted enough supporters' signatures and some of the names she did sent in belonged to dead people.

Rwigara denied the allegations.

"They are accused of tax evasion and secondly Diane Rwigara is accused of using fake documents while she was gathering signatures for (her) presidential candidacy," Theos Badege, police spokesman, told reporters on Monday.

Police said they had a warrant issued by a prosecutor to arrest them.

Rwigara, a 35-year-old accountant, has repeatedly accused Kagame of stifling dissent and criticised his Rwandan Patriotic Front's near total hold on power.

Kagame won last month's election with 98.8 percent of the vote.

Kagame won international praise for presiding over a peaceful and rapid economic recovery in Rwanda since the 1994 genocide, when an estimated 800,000 people Tutsis and moderate Hutus were killed.

But he has also faced increased criticism for what human rights groups say are widespread abuses, a muzzling of independent media, and suppression of political opposition.

Rwigara claimed that she was being held under house arrest before Monday's police action.

"Tell us why we are being arrested? Why should we go to the police while you have confined us to this place and took away all our money without leaving us any?" Rwigara said as she and her family were being taken away.

Asked about this, Badege, the police spokesman, said that earlier police had only searched Rwigara's home and taken a few items and money away in line with the law, adding that this was a clear application of the law.